Need to change pivot points during animation
If what you want to do is a series of rotations for your triangle, what you could do is use Child Of constraints with some empties:

Create an empty at the first pivot point of the triangle, give your triangle a Child Of constraint with the empty as Target, press the Set Inverse button, keyframe the empty:



Rotate the empty, keyframe the rotation, put the 3D cursor on the second pivot point, create an empty, give your triangle a second Child Of constraint with this second empty as Target and Set Inverse, keyframe this empty:




Rotate this second empty, keyframe.